memcg: cgroup_write_event_control() now knows @css is for memcg

@css for cgroup_write_event_control() is now always for memcg and the
target file should be a memcg file too.  Drop code which assumes @css
is dummy_css and the target file may belong to different subsystems.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 02dae32926680f3f472c3434576a7405a782c31c..d00368110b08367f6bf4d06e43ea847d0f5d4c73 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6056,10 +6056,10 @@ static void cgroup_event_ptable_queue_proc(struct file *file,
  * Input must be in format '<event_fd> <control_fd> <args>'.
  * Interpretation of args is defined by control file implementation.
  */
-static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
+static int cgroup_write_event_control(struct cgroup_subsys_state *css,
                                      struct cftype *cft, const char *buffer)
 {
-       struct cgroup *cgrp = dummy_css->cgroup;
+       struct cgroup *cgrp = css->cgroup;
        struct cgroup_event *event;
        struct cgroup_subsys_state *cfile_css;
        unsigned int efd, cfd;
@@ -6082,6 +6082,7 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
        if (!event)
                return -ENOMEM;
 
+       event->css = css;
        INIT_LIST_HEAD(&event->list);
        init_poll_funcptr(&event->pt, cgroup_event_ptable_queue_proc);
        init_waitqueue_func_entry(&event->wait, cgroup_event_wake);
@@ -6117,23 +6118,17 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
                goto out_put_cfile;
        }
 
-       if (!event->cft->ss) {
-               ret = -EBADF;
-               goto out_put_cfile;
-       }
-
        /*
-        * Determine the css of @cfile, verify it belongs to the same
-        * cgroup as cgroup.event_control, and associate @event with it.
-        * Remaining events are automatically removed on cgroup destruction
-        * but the removal is asynchronous, so take an extra ref.
+        * Verify @cfile should belong to @css.  Also, remaining events are
+        * automatically removed on cgroup destruction but the removal is
+        * asynchronous, so take an extra ref on @css.
         */
        rcu_read_lock();
 
        ret = -EINVAL;
-       event->css = cgroup_css(cgrp, event->cft->ss);
-       cfile_css = css_from_dir(cfile.file->f_dentry->d_parent, event->cft->ss);
-       if (event->css && event->css == cfile_css && css_tryget(event->css))
+       cfile_css = css_from_dir(cfile.file->f_dentry->d_parent,
+                                &mem_cgroup_subsys);
+       if (cfile_css == css && css_tryget(css))
                ret = 0;
 
        rcu_read_unlock();
@@ -6145,7 +6140,7 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
                goto out_put_css;
        }
 
-       ret = event->cft->register_event(event->css, event->cft,
+       ret = event->cft->register_event(css, event->cft,
                        event->eventfd, buffer);
        if (ret)
                goto out_put_css;
@@ -6162,7 +6157,7 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
        return 0;
 
 out_put_css:
-       css_put(event->css);
+       css_put(css);
 out_put_cfile:
        fdput(cfile);
 out_put_eventfd: